Takahashi
FS-85 Mini (visual) Review
Takahashi’s FSQ-85 is a popular
deep-sky imaging scope, but this mini review focuses on using it visually. That’s
because I haven’t yet had the opportunity to try imaging with it, but also
because there’s not much info’ around on the visual performance of the FSQ-85.
And it turns out that Takahashi have put lots of effort into making sure it
works well with an eyepiece (unlike many imaging scopes).
This is the latest in a series of mini
reviews of scopes that I’ve spent lots of time with, but haven’t been able to
put through my complete review process.
I’ll hopefully be able to add example
deep-sky images in due course.
(A big thanks to Richard Lynch for
giving me access to his FSQs and for some of the images in this review).
At
A Glance
|
Telescope |
Takahashi
FSQ-85 |
|
Aperture |
85mm |
|
Focal
Length |
450mm / 680mm
w/ 1.5x extender |
|
Focal
Ratio |
F5.3 |
|
Length |
~370mm w/o
visual back |
|
Weight |
3.6 Kg |
Data from Tak,
Me as usual.
Design
and Build
Like the current FSQ-106 and FSQ-85, the
original FSQ-106N was a quadruplet Petzval, but with a crown of mineral
fluorite instead of the high-fluoride glass in the later ED models. That
original version is distinguished by a longer OTA with a blue serial plate
(below).
The FSQ-85ED, aka Baby-Q, came along
later as a replacement for the discontinued doublet Sky90 portable imaging
scope. There’s not much difference in size (or weight) between the Sky90 and
the FSQ-85, but the FSQ-106 is much heavier.
Takahashi have now extended the ‘Q-for-quadruplet’
tag to two other scopes – the FS-60Q and FOA-60Q – but both are existing
doublets with converter modules.
For a few years Takahashi also produced
an FSQ-130ED, but it was hugely expensive.
The original fluorite FSQ-106N.
Three Takahashi imaging scopes:
FSQ-106, FSQ-85 and FS-60C (actually an FS-60Q without its extender).
FSQs and Sky90.
Optics
The
quadruplet Petzval was an early flat-field camera lens design later popularised
for amateur telescopes by Al Nagler of Tele Vue, who developed a series them
starting with the Genesis.
Compared
with Tele Vue’s designs, Takahashi’s are more sophisticated in both optics and
engineering, but the principal is the same.
The Petzval
combines a long-focal-length objective with a doublet reducer/flattener at the
rear that roughly halves the focal length. It’s a design that produces a fast
and well-corrected optical system, but with the downside of vignetting
(mitigated if the Petzval lens is expensively oversized, as it is in the 106
and Tele Vue’s imaging-system Nagler-Petzvals too).
In the case
of the FSQ-85, the objective is a front-surface ED doublet of about ~F11, so
the final focal length is 450mm (~F5.3). Unlike the Tele Vue Petzvals, both Takahashi’s ED variants employ a very large
air gap between the Petzval elements to improve correction. The Petzval lens is
mounted in the rear tube section in the 85.
So is the
FSQ-85 just a scaled down FSQ-106ED, then? Not quite: it seems to a be a
simpler design. Differences include:
· The FSQ-106ED has a more sophisticated objective
with a larger air gap and collimation adjustment screws
· The FSQ-106ED uses two ED glass elements, one in
the objective the other in the Petzval lens
· The FSQ-106ED’s larger Petzval lens gives better
coverage (the front Petzval element isn’t much smaller than the objective!)
· The FSQ-106ED has a different tube design and a
larger focuser
Overall,
this means that the 106 has better coverage and smaller spot sizes (below) off-axis
than the 85, possibly better correction too despite its larger aperture, but at
much higher cost and almost double the weight.
Note: The
original FSQ-85 was designed for imaging with an APS-C sized sensor and starts
to suffer some residual field curvature and astigmatism by ~12mm off-axis.
Consequently, Takahashi developed a dedicated 1.01X flattener for the FSQ-85
that gives good star images out to 22mm off-axis and 60% illumination as well.
The latest
‘EDP’ version (which has a slightly different focuser/rotator from the one
here) ships with the Flattener in European markets.
Tube
The FSQ-85
has a 95mm tube like the FC-100D, with a 114mm diameter retracting dew shield. Build
quality and finish is superb as usual.
Tak’ quote
535mm length with the dewshield retracted, but that’s with extension tubes
fitted. With all the visual back components unthreaded, the FSQ-85 packs down to
less than 400mm – shorter than a TV-85 or AP Stowaway and just a little longer
than the tiny Sky-90. It’s easily carry-on portable.
The FSQ-85 feels
weighty for its compact dimensions, but at 3.6 Kg it is much the same as other
imaging apochromats in this size range.
In theory the
tube separates into two sections on a threaded joint, but – unlike say an
FC-100D – doesn’t need disassembly to fit in an airline case.
Focuser
The focuser
is a heavy duty rack-and-pinion unit, with a wide drawtube, a microfocuser, a larger pinion assembly than most and a
camera-angle-adjuster, all standard equipment.
Tak’s focusers
with their cast bodies and drawtubes are different from high-end units from the
likes of Starlight Instruments made on a CNC machine. At their best, Takahashi’s
are every bit as precise and perhaps even smoother, but can wear if subjected
to heavy loads.
Despite
being a robust unit, this one did exhibit just a little of the image shift that
plagues some (but not all) Takahashi focusers, as usual likely the result of
wear to the bushes.
Mounting
On the night
I did most of my viewing with the FSQ-85 it was mounted on a Vixen APZ – a
small alt-az mount somewhere between a Porta and an
AZ8. The combination was rock-solid, even at the highest powers, an advantage
of a light and compact OTA like the FSQ.
For imaging,
the FSQ-85 would be fine on a small equatorial, unlike its larger sibling.
Accessories
The FSQ-85
shares the good-but-costly QE0.73x reducer with the FSQ-106. On the 85 it drops
the focal length to just 327mm at F3.8 with an image circle of 60% at 44mm.
A cheaper
option would be the 1.01x flattener which the new EDP model gets as standard. This
offers the same 44mm/60% image circle as the reducer, but at 455mm focal length
(F5.4) - sufficient for many.
For visual
use, Takahashi offer a 1.5x extender (the FSQ-106’s gets a different 1.6x
Extender-Q) to sharpen the optics and improve correction. It was used for the
planetary viewing described in this review.
In
Use – Daytime
As Tele Vue
knew thirty years and more ago, flat-field Petzvals
make great terrestrial scopes with their wide flat well-corrected field. Make
no mistake, no prismatic scope gives the sharp, aberration-free high-power
(100X plus) terrestrial views the FSQ-85 is capable of. My usual test of
viewing silhouetted branches yields minimal fringing.
In
Use – Observing the Night Sky
General
Observing Notes
The FSQ-85
was very easy to use visually, with its short length and rotator allowing a comfy
eyepiece position at all times. Cool down was fast (see below) compared with
the larger scopes alongside and didn’t seem worse than the FC-100DC.
The focuser
coped well with heavy eyepieces, but I did notice some image shift at high
power on this example.
In terms of
false colour and polychromatic-Strehl, the objective
performs as I’d expect a regular 85mm F11 FPL-53 doublet should, which means
very little false colour, no softness in the red and low bloat on hot stars for
imaging.
Cool
Down
I noted
surprisingly rapid cool-down, in spite of the Petzval design which traps air
between the elements. I also noted that the FSQ-106 alongside cooled much more
gradually.
Star
Test
The star
test was excellent, with evenly illuminated and spaced rings either side of
focus and in-focus diffraction rings few and dim
The
Moon
The FSQ-85
gave exceptionally sharp and high-contrast views of limb mountains just after
full Moon, picked out against black space with no false colour fringing and
little flare.
Mars
Mars on
opposition day 2022 showed a very sharply defined disk (17 arcsecs across) with
the 4mm setting on Nagler Zoom giving 170x with the 1.5 extender. There was
absolutely no false colour in or out of focus, no flare of dark red light that
you often get with ED doublets and no softness.
I noted the
dark area of Mare Acidalium in the north east. In the
south, was a dark east-west strip comprising Mare Erythraeum
in the east and Mare Sirenum in the west, with a
lighter area in the middle that’s actually the Solis Lacus
‘Eye of Mars’ area, but not resolvable as such at this aperture.
I thought
the view compared very favourably with the AP Stowaway’s the previous night, just
slightly lower in contrast to the FC-100D on the same night (to be expected due
to the smaller aperture).
Jupiter
The FSQ-85
gave a perfectly sharp, false-colour free view of Jupiter with the 5mm and 4mm settings
on a Nagler Zoom giving 136x and 170x respectively. I noted lots of cloud belt
detail, including thickness variations in NEB and SEB, polar cap banding and at
least one other cloud belt. Very impressive for this aperture.
This
is what prompted me to write this review, because I just hadn’t expected the
FSQ-85 to perform well on planets at all.
Deep
Sky
Like Tele
Vue’s Petzvals, when combined with a wide-field
eyepiece like a Nagler, Delos or Ethos, the little FSQ has real wow factor for
extended DSOs, with pinpoint stars across the whole flat field when turned on
the Double Cluster and Stock2, or M36-38 in Auriga.
The Baby-Q
gave an excellent split of the Double Double at 169x
with the 4mm setting on the Nagler Zoom, with the small and perfect stellar
diffraction patterns helping.
Summary
I expected
the FSQ-85 to be a good imaging machine and knew it was small and compact, but
I was surprised at what a fine visual scope it proved to be, even at high
powers (albeit with the dedicated extender).
I was
particularly surprised at the very fine planetary views it gave for an imaging
refractor – very comparable to the AP Stowaway and significantly better on Mars
than a TV-85.
Compared with
some imaging scopes that are really just camera lenses, the FSQ-85 makes a fine
double-duty tool for visual astronomy too, which could help justify its high
price.
You knew the FSQ-85 produces good subs
for imaging, but might be surprised at how well it performs visually,
especially when combined with the dedicated extender.
FSQ-85 set on Mars at opposition.